JohnK,
I think your best bet would be a large settling tank coming from the fish tank. Use the gravity drain from fish tank to settling tank like this.
You could remove virtually all your solids with the benefit of using the settling tank as a fry trap. Simply put a very large drain pipe at the top of your settling tank (twice the size or more of the inlet) and place a fine screen on it. You'll suck up your fry INTO the settling chamber and relative safety for easy removal while still removing large quantities of fish waste that you could "flush" daily via a bottom valve in your settling tank after removing any fry. You could then run the outlet of the settling tank to a bio filtration system and sump system. Place a high flow pump with float valve in your bio filter (a good basement sump pump that can handle solids would do) that will return water as needed and at a very high flow back to the fish tank. You can even get relatively inexpensive battery backups that use a car battery for sump pumps to protect you against power failure. You could take it a step further and add a third container with aquatic plants after your bio filter and prior to the pump to remove nitrites/nitrates. Basically, an aquaponic setup but using aquatic plants instead of garden veggies.
Since you have a non-syphoning gravity drain on your fish tank you don't have the risk of an overflow or total tank drain in your system in the event of a pump malfunction, which is obviously quite important.
This system works quite well, uses very little power and requires minimal maintenance. I've set several of them up this way and similar ways with excellent results.
